One method of determining the distance to an object is to illuminate the object with pulsed light and compare the phase of the reflected light pulses with the phase of the light pulses used to illuminate the object. Typically, distance measuring devices employing this and similar methods employ charge-coupled devices (CCD's) to sense the reflected light, and complimentary metal oxide semiconductor (CMOS) circuitry to implement associated circuitry such as controllers, analog-to-digital (A/D) converters, and the like.
In operation, the CCD's receive the reflected light and generate an amount of charge related to the amount of light received. This charge is stored over particular periods of time, sometimes referred to as integration periods. Between integration periods, the CCD's dump stored charge to a storage node. The amount of charge stored in a node corresponds to the amount of charge generated by a CCD during a particular integration period, and can be compared to the amount of charge corresponding to a different integration period to determine a phase difference between the light used to illuminate the object and light reflected from the object back to the CCD sensor. In some cases, different CCD's are used to generate charge during different integration periods instead of using a single CCD to generate charge for all integration periods.
CCD's, however, use a relatively large amount of power, are more complicated to fabricate, and require more complex power supplies than, for example, CMOS circuitry. In addition, CCD's are incompatible with CMOS circuitry, and CMOS circuitry is often used in manufacturing semiconductor devices. Because of this incompatibility, when CCD's are used in distance determining devices, complex interface circuits, companion chips, etc. must be built so that the CMOS circuitry and the CCD circuitry can be used together. What is needed, therefore, is a sensor capable of easier integration with low cost CMOS technologies, without requiring the higher power consuming circuits of CCD technologies, and avoiding costly fabrication of complex interface circuitry.